Fiber structure and method for manufacturing same

ABSTRACT

A fiber structure contains polyester fibers 1 and a hydrophilic polyester resin treatment agent, wherein part 2a of a molecule 2 of the hydrophilic polyester resin treatment agent is absorbed in at least part of the polyester fibers 1, and the remainder 2b of the molecule extends along the surface of the polyester fibers 1 to hydrophilize the surface. The fiber structure has the properties below: (1) antifouling properties of grade 4 or higher according to the gray scale assessment determined by applying 200 g of muddy water, which is a mixture of normal staining soil and sand and distilled water at a ratio of 1:1, to the fiber structure, followed by standing for 24 hours, washing, and drying; (2) water absorbability of 10 seconds or less according to the falling-drop method; and (3) diffusivity of 55 minutes or less according to the diffusible residual water content test (dropping 0.6 mL of water). Thus, the present invention provides a fiber structure not involving curing to keep a good texture while having high antifouling properties, water absorbability, diffusivity, etc.

TECHNICAL FIELD

The present invention relates to a fiber structure having high antifouling properties, water absorbability, diffusivity, and the like, and a method for producing the same.

BACKGROUND ART

Polyester fibers are hydrophobic, and their antifouling properties, water absorbability, and diffusivity are low without treatment. Clothes using these fibers are uncomfortable to wear. To cope with these problems, various proposals have been made. Patent Document 1 proposes applying a hydrophilic polymer treatment agent to a fiber structure containing polyester fibers, followed by curing with a metal salt catalyst. Patent Document 2 proposes applying a hydrophilic oil-repellent polymer treatment agent to a fiber structure containing polyester fibers, followed by curing with a metal catalyst. Patent Document 3 proposes applying a hydrophilic polymer treatment agent and a bacteriostatic agent to a fiber structure containing polyester fibers, followed by curing with low-temperature plasma.

PRIOR ART DOCUMENTS Patent Documents

Patent Document 1: JP 2013-072164A

Patent Document 2: JP 2012-012718A

Patent Document 3: JP 2010-121230A

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

All the above conventional techniques involve curing with a catalyst, plasma, etc., after application of a treatment agent to the fiber structure containing polyester fibers. However, curing makes the texture hard and does not allow the fiber structure to have satisfactory antifouling properties, water absorbability, diffusivity, and the like.

To solve the above conventional problems, the present invention provides a fiber structure not involving curing to keep a good texture while having high antifouling properties, water absorbability, diffusivity, and the like.

Means for Solving Problem

A fiber structure of the present invention is a fiber structure containing polyester fibers and a hydrophilic polyester resin treatment agent,

-   -   wherein part of a molecule of the hydrophilic polyester resin         treatment agent is absorbed in at least part of the polyester         fibers, and the remainder of the molecule extends along the         surface of the polyester fibers to hydrophilize the surface, and     -   wherein the fiber structure has the properties below:     -   (1) antifouling properties of grade 4 or higher according to the         gray scale assessment specified in JIS L 0805 (2005), determined         using the fiber structure prepared by applying 200 g of muddy         water, which is a mixture of normal staining soil and sand and         distilled water at a ratio of 1:1, to the fiber structure,         followed by standing for 24 hours, washing according to the         method 103 specified in JIS L 0217 (1995), and drying;     -   (2) water absorbability of 10 seconds or less according to the         falling-drop method specified in JIS L 1907 (2004); and     -   (3) diffusivity of 55 minutes or less according to the         diffusible residual water content test, method A-1, specified in         ISO 17617 (dropping 0.6 mL of water).

A method for producing the fiber structure of the present invention includes:

-   -   subjecting an untreated fiber structure to immersion heating in         an aqueous solution containing a hydrophilic polyester resin         treatment agent molecule to make part of the molecule of the         hydrophilic polyester resin treatment agent absorbed in at least         part of the polyester fibers and the remainder of the molecule         extend along the surface of the polyester fibers to hydrophilize         the surface.

Effect of the Invention

The fiber structure of the present invention is a fiber structure containing polyester fibers and a hydrophilic polyester resin treatment agent, wherein part of a molecule of the hydrophilic polyester resin treatment agent is absorbed in at least part of the polyester fibers, and the remainder of the molecule extends along the surface of the polyester fibers to hydrophilize the surface. Thus, it is possible to provide a fiber structure not involving curing to keep a good texture while having high antifouling properties, water absorbability, diffusivity, and the like. Further, by the combined use of an antibacterial agent, the surface of the fiber structure is coated with at least part of the hydrophilic polyester resin treatment agent; besides, the antibacterial agent is fixed to the surface of the hydrophilic polyester resin treatment agent and/or at least part of the antibacterial agent is absorbed in at least part of the polyester fibers. Thus, durable antibacterial properties are obtained.

Further, the method for producing the fiber structure according to the present invention includes subjecting an untreated fiber structure to immersion heating in an aqueous solution containing the hydrophilic polyester resin treatment agent molecule to make part of the molecule of the hydrophilic polyester resin treatment agent absorbed in at least part of the polyester fibers and the remainder of the molecule extend along the surface of the polyester fibers to hydrophilize the surface. Thus, the fiber structure of the present invention can be reasonably produced with efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a state in which part of a molecule of a hydrophilic polyester resin treatment agent is absorbed in part of polyester fibers according to an embodiment of the present invention, and the remainder of the molecule extends along the surface of the polyester fibers to hydrophilize the surface.

FIG. 2 is a schematic cross-sectional view illustrating a state in which an antibacterial agent is fixed to the surface of the hydrophilic polyester resin treatment agent according to another embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating a state in which an antibacterial agent is absorbed in the polyester fibers according to still another embodiment of the present invention.

DESCRIPTION OF THE INVENTION

The hydrophilic polyester resin treatment agent used in the present invention functions like a disperse dye such that at least part of the treatment agent is absorbed in the polyester fibers (exhaustive diffusion). For example, the hydrophilic polyester resin treatment agent is a linear copolymer in which polyester groups and hydrophilic groups are linked together at their terminals. The hydrophilic polyester resin treatment agent is preferably a block copolymer. The molecular weight is preferably 5000 to 8000, and more preferably 6000 to 7000. The weight ratio of the polyester group to the hydrophilic group is preferably 90/10 to 10/90, and more preferably 60/40 to 20/80. Examples of the hydrophilic group include polyethylene glycol, sodium 5-sulfoisophthalate, and trimellitic anhydride, and polyethylene glycol is more preferred. For example, the treatment agent may be KMZ-902 (product number) manufactured by TAKAMATSU OIL & FAT CO., LTD.

When the fiber structure containing polyester fibers is subjected to immersion heating in an aqueous solution containing the hydrophilic polyester resin treatment agent, at least part of the polyester group of the hydrophilic polyester resin treatment agent molecule is absorbed in at least part of the polyester fibers, for example, an amorphous portion of the polyester fibers, and the hydrophilic group of the molecule extends along the surface of the polyester fibers to hydrophilize the surface. The immersion heating enlarges the pores in the amorphous portion of the polyester fibers at a temperature equal to or higher than the glass transition point, causing at least part of the polyester group to enter the pores. After the immersion heating, the pores in the amorphous portion return to the original size as the temperature of the polyester fibers drops to the glass transition point or lower. Thus, at least part of the polyester group is contained in the polyester fibers. This mechanism provides a very strong bonding and a soft texture without impairing the functionality. The molecular weight of two monomers (dimer) as the base of the polyester group that can enter the pores in the amorphous portion of the polyester fibers is 200 to 1000, and more preferably 250 to 800. The polyester group is a polymer in which a plurality of monomers such as polyethylene terephthalate are joined together. The polyester group is not straight but three-dimensional, and whether or not the polyester group can enter the pores can be determined appropriately from the molecular weight of the dimer. If the molecular weight is smaller than 200, the dimer as the base of the polyester group is smaller than the pores in the amorphous portion, and the polyester group easily escapes from the pores in the amorphous portion of the polyester fibers, which deteriorates the durability. If the molecular weight is larger than 1000, the dimer as the base of the polyester group is larger than the enlarged pores in the amorphous portion at a temperature equal to or higher than the glass transition point, and the polyester group cannot enter the pores in the amorphous portion. The hydrophilic polyester resin treatment agent containing polyester groups of a preferable molecular weight eliminates a curing process using a curing catalyst, electron beam, plasma irradiation, etc. Thus, it is possible to provide a fiber structure having highly durable antifouling properties, water absorbability, and diffusivity, while keeping a good texture.

The fiber structure has the following properties.

-   -   (1) Antifouling properties: 200 g of muddy water, prepared by         mixing normal staining soil and sand and distilled water at a         ratio of 1:1, is applied to the fiber structure, which is then         left for 24 hours, washed according to the method 103 specified         in JIS L 0217 (1995), and dried. The gray scale assessment         specified in JIS L 0805 (2005) of the dried fiber structure is         grade 4 or higher, and preferably grade 4 and grade 5.     -   (2) Water absorbability: The time required for the fiber         structure to absorb water is 10 seconds or less, preferably 5         seconds or less, more preferably 3 seconds or less, and further         preferably 1 second or less according to the falling-drop method         specified in JIS L 1907 (2004).

(3) Diffusivity: The diffusivity of the fiber structure is 55 minutes or less, and the diffusivity of the knitted fabric is preferably 55 minutes or less and that of the woven fabric is preferably 45 minutes or less according to the diffusible residual water content test, method A-1, specified in ISO 17617 (dropping 0.6 mL of water).

The following describes the reasons why the fiber structure has such properties.

-   -   (1) Antifouling properties: By hydrophilizing the surface of the         fiber structure, the affinity with mud stains, which are oily         stains, decreases, reducing the contact area. This causes the         rolling-up phenomenon to occur easily during water washing and         removes mud stains easily. Further, by hydrophilizing the         surface of the fiber structure, the affinity between water and         the fiber structure during water washing increases. This allows         water to easily enter between mud stains and the fiber structure         and removes the mud stains easily.     -   (2) Water absorbability: By hydrophilizing the surface of the         fiber structure, the affinity between the fiber structure and         water increases, enhancing the water absorbability.     -   (3) Diffusivity: By hydrophilizing the surface of the fiber         structure, the affinity between the fiber structure and water         increases, enhancing the water absorbability. Because of this,         the diffusivity also increases in the horizontal direction of         the fiber structure. The increased diffusivity increases the         evaporation amount of water, enhancing the rapid drying         properties of the fiber structure.

The antibacterial properties of the fiber structure, determined according to an antibacterial activity value measured based on the antibacterial property test specified in JIS L 1902 (2015), are preferably 2.2 or more, more preferably 3 or more, and further preferably 3.5 or more. Examples of the antibacterial agent usable in the present invention include silver-based, silver ion-based, zinc-based, silane (silicon)-based, quaternary ammonium ion salt-based, and biguanide-based antibacterial agents.

Antibacterial agents such as zinc-based, silane (silicon)-based, quaternary ammonium ion salt-based, and biguanide-based antibacterial agents can adsorb on the polyester fibers through immersion heating without relying on resin binders and keep the effects of the hydrophilic polyester resin treatment agent of the antifouling properties, water absorptivity, and diffusivity. The immersion heating of the polyester fibers enlarges the pores in the amorphous portion of the polyester fibers at a temperature equal to or higher than the glass transition point, causing at least part of the polyester group of the hydrophilic polyester resin treatment agent and the antibacterial agent to simultaneously enter the pores. After the immersion heating, the pores in the amorphous portion return to the original size as the temperature of the polyester fibers drops to the glass transition point or lower. Thus, at least part of the polyester group and the antibacterial agent are contained in the polyester fibers. The containment of the at least part of the polyester group and the antibacterial agent in the pores in the amorphous portion further strengthens the bonding of the polyester group and the bonding of the antibacterial agent to the polyester fibers. The molecular weight of the antibacterial agent to be bonded to the amorphous portion of the polyester fibers is 200 to 1000, and more preferably 250 to 800. Antibacterial agents having a molecular weight smaller than the above range result in poor durability, while those having a molecular weight larger than the above range result in poor adsorption. Specifically, if the molecular weight is smaller than 200, the size of the antibacterial agent is smaller than the size of the pores in the amorphous portion, and the antibacterial agent easily escapes from the pores in the amorphous portion of the polyester fibers, which deteriorates the durability. If the molecular weight is larger than 1000, the size of the antibacterial agent is larger than the size of the enlarged pores in the amorphous portion at a temperature equal to or higher than the glass transition point, and the antibacterial agent cannot enter the pores in the amorphous portion. For example, zinc pyrithione having a molecular weight of about 317 can be easily bonded to the amorphous portion of the polyester fibers and provides good durability.

The silver ion-based antibacterial agent is soluble together with resin in an aqueous solution. The resin is preferably an acrylic resin. The pH of the aqueous solution is alkaline or acidic. The aqueous solution is, for example, an aqueous ammonia solution. The silver ion content of the silver ion-based antibacterial agent in the aqueous solution is 300 ppm or less and 1 ppm or more per fiber weight, and preferably 200 ppm or less and 10 ppm or more. The resin dissolved in the aqueous solution needs to be 600 ppm or less and 2 ppm or more per fiber weight, and preferably 400 ppm or less and 20 ppm or more. By heating the aqueous solution of the silver ion-based antibacterial agent, ammonia and the like are volatilized, neutralizing the aqueous solution. When the aqueous solution is rendered neutral, the dissolved resin is polymerized and adheres to the polyester fiber structure. The amount of the resin is very small, and hence the resin adheres to the polyester fiber structure sparsely. The resin sparsely adhering to the polyester fiber structure carries silver ions and imparts antibacterial properties to the fiber structure. Since the resin sparsely adheres to the polyester fibers and does not cover the entire surface, gaps are present between the antibacterial agent. Thus, the antibacterial agent does not impair the effects of the hydrophilic polyester resin treatment agent of the antifouling properties, water absorptivity, and diffusivity. Further, since the silver ions have a small molecular weight of about 47, it is preferable to adhere the silver ions to the surface of the fiber structure by padding, rather than the penetration of the silver ions into the amorphous portion of the polyester fibers by immersion. This is because the favorable molecular weight of the antibacterial agent that is suitable for the size of the pores in the amorphous portion of the polyester fibers ranges from 200 to 1000, and the molecular weight of the silver ions is smaller than 200, which allows the silver ions easily to escape from the pores in the amorphous portion of the polyester fibers and deteriorates the durability. To avoid this, resin is dissolved in the aqueous solution of the silver ion-based antibacterial agent to make the polymerized resin carry the silver ions and intervene between the polyester fibers and the silver ions for enhanced bonding durability. At least part of the silver ion-based antibacterial agent may be absorbed in the amorphous portion of the polyester fibers. Generally, the bonding between the polyester fibers and the antibacterial agent is achieved using a resin binder such as urethane or silicon. For example, conventional silver-based antibacterial agents have a silver metal content of 7000 ppm or less and 1000 ppm or more per fiber weight. The resin binder is insoluble in an aqueous solution, and the content thereof is at least 1000 ppm or more per fiber weight. The resin binder of this amount covers the entire surface of the fiber structure through application of the antibacterial agent. Thus, the conventional antibacterial agents tend to impair the effects of the hydrophilic polyester resin treatment agent of the antifouling properties, water absorptivity, and diffusivity.

According to the method for producing the fiber structure of the present invention, the fiber structure is subjected to the immersion heating in the aqueous solution containing the hydrophilic polyester resin treatment agent molecule to make part of the treatment agent absorbed in at least part of the polyester fibers and the remainder extend along the surface of the polyester fibers to hydrophilize the surface. Thus, it is possible to provide a fiber structure having high antifouling properties, water absorbability, and diffusivity while keeping a good texture.

In the immersion heating, it is preferred that the fiber structure is immersed in the aqueous solution containing the hydrophilic polyester resin treatment agent, heated from room temperature to 110° C. to 135° C. and kept at the temperature for 20 to 120 minutes, followed by cooling, and water washing. After water washing, tentering may be performed with heat in accordance with an ordinary method.

For antibacterial finishing, there are the following two methods in the present invention.

-   -   (1) The antibacterial agent is added in the same bath with the         aqueous solution containing the hydrophilic polyester resin         treatment agent in the immersion heating of the fiber structure         (same bath treatment).     -   (2) After the immersion heating of the fiber structure in the         aqueous solution containing the hydrophilic polyester resin         treatment agent, the fiber structure is padded with an aqueous         solution containing an antibacterial agent and heated         (sequential treatment).     -   By the same bath treatment or the sequential treatment, the         antibacterial agent is retained in the hydrophilic polyester         resin treatment agent, and durable antibacterial properties are         obtained.

In the immersion heating, a disperse dye may also be added for the same bath treatment. This is because the hydrophilic polyester resin treatment agent in the present invention is used under the heating conditions similar to those for the disperse dye.

The following describes a knitted fabric for clothing according to a preferable embodiment of the present invention using drawings. In the drawings, the same reference numerals are assigned to the same components. FIG. 1 is a schematic cross-sectional view illustrating a state in which the hydrophilic polyester resin treatment agent is absorbed in the polyester fibers according to an embodiment of the present invention. At least part 2 a of the polyester group of a hydrophilic polyester resin treatment agent molecule 2 is absorbed in the amorphous portion of a polyester fiber 1, and a hydrophilic group 2 b extends along the surface of the polyester fiber 1. Thus, highly durable antifouling properties, water absorbability, and diffusivity are obtained.

FIG. 2 is a schematic cross-sectional view illustrating a state in which the hydrophilic polyester resin treatment agent 2 is absorbed in the polyester fiber 1 according to another embodiment of the present invention. FIG. 2 differs from FIG. 1 in that an antibacterial agent 3 is fixed to the hydrophilic group 2 b of the hydrophilic polyester resin treatment agent molecule 2. This state is obtained by subjecting the fiber structure to the immersion heating in an aqueous solution containing the hydrophilic polyester resin treatment agent, followed by padding with an aqueous solution containing the antibacterial agent, and heating (sequential treatment).

FIG. 3 is a schematic cross-sectional view illustrating a state in which the hydrophilic polyester resin treatment agent is absorbed and diffused in the polyester fiber according to still another embodiment of the present invention. FIG. 3 differs from FIG. 2 in that the antibacterial agent 3 is absorbed in the polyester fiber 1 together with at least part of the polyester group of the hydrophilic polyester resin treatment agent molecule 2. This state is obtained by adding the antibacterial agent in the same bath with the aqueous solution containing the hydrophilic polyester resin treatment agent at the time of the immersion heating of the fiber structure (same bath treatment).

EXAMPLES

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to the following examples.

The evaluation methods are as described below.

Mass (Mass Per Unit Area) of Knitted Fabric

The mass was measured according to the method A specified in JIS L 1096.

Antifouling Properties

The antifouling properties are determined according to the gray scale assessment specified in JIS L 0805 (2005) using a 10 cm×10 cm fiber structure prepared by applying 200 g of muddy water, which is a mixture of normal staining soil and sand and distilled water at a ratio of 1:1, to the fiber structure, followed by standing for 24 hours, washing according to the method 103 specified in JIS L 0217 (1995), and drying. The fiber structure is ranked into ten grades from grade 1 to grade 5. The higher the grade, the better the antifouling properties.

Water Absorbability

The time required for the fiber structure to absorb water is measured according to the falling-drop method specified in JIS L 1907 (2004).

Diffusivity

The diffusivity is measured according to the diffusible residual water content test, method A-1, specified in ISO 17617:2014 (dropping 0.6 mL of water).

Antibacterial Properties

The antibacterial properties are determined according to an antibacterial activity value measured based on the antibacterial property test specified in JIS L 1902 (2015).

Example 1 1. Knitted Fabric

A knit was made with a circular knitting machine using polyester (PET) multifilament yarns (yarns having a total fineness of 40 D (denier), 36 filaments, the used ratio 5% by weight; yarns having a total fineness of 50 D, 72 filaments, the used ratio 60% by weight; and yarns having a total fineness of 60 D, 48 filaments, the used ratio 35% by weight). The mass (mass per unit area) of the obtained knitted fabric was 80 g/m².

2. Hydrophilic Treatment (1) Agents

Hydrophilic polyester resin: KMZ-902 (product number) manufactured by TAKAMATSU OIL & FAT CO., LTD., 5% o.w.f (abbreviation of on the weight of fiber)

Antibacterial agent: commercially available zinc pyrithione-based compound, 1% o.w.f

(2) Treatment Conditions (Same Bath Treatment)

The knitted fabric was immersed in an aqueous solution containing the above agents, heated from room temperature to 130° C. at 2° C./minute and maintained at 130° C. for 60 minutes, followed by cooling, water washing, drying, and tentering and heat setting.

Table 1 below summarizes the results.

Example 2 1. Knitted Fabric

A knit was made with a circular knitting machine using polyester (PET) multifilament yarns (yarns having a total fineness of 40 D, 36 filaments, the used ratio 5% by weight; yarns having a total fineness of 75 D, 36 filaments, the used ratio 74% by weight; and yarns having a total fineness of 100 D, 72 filaments, the used ratio 21% by weight). The mass (mass per unit area) of the obtained knitted fabric was 120 g/m².

2. Hydrophilic Treatment (1) Agents

Hydrophilic polyester resin treatment agent: KMZ-902 (product number) manufactured by TAKAMATSU OIL & FAT CO., LTD., 5% o.w.f (abbreviation of on the weight of fiber)

Antibacterial agent: commercially available silver ion-based compound, 3% o.w.f

(2) Treatment Conditions (Sequential Treatment)

The knitted fabric was immersed in an aqueous solution in which the hydrophilic polyester resin treatment agent was dispersed, heated from room temperature to 130° C. at 2° C./minute and maintained at 130° C. for 60 minutes, followed by cooling, water washing, and drying.

Next, the knitted fabric was padded at the pick-up rate of 100% with an aqueous solution in which the antibacterial agent was dispersed, and heated at 150° C. for 120 seconds for tentering and heat setting. Table 1 summarizes the results.

TABLE 1 Example 1 Example 2 Antifouling properties grade 4-5 grade 4 Water absorbability less than 1 second 1 second JIS L1907 (2004) Diffusivity 51.5 minutes 28.4 minutes ISO 17617, A-l (dropping 0.6 mL) Antibacterial properties 3 5.9 JIS L1902 (2015)

The knitted fabrics of the examples after the above treatment resulted in the antifouling properties of grade 4 or higher, the water absorbability of 10 seconds or less, the diffusivity of 55 minutes or less (knitted fabric), and the antibacterial properties of 2.2 or more, which were all acceptable. The knitted fabrics were also soft and had a good texture.

INDUSTRIAL APPLICABILITY

The fabrics of the present invention are suitable for innerwear such as sports shirts, T-shirts, inner shirts, briefs, tights, general shirts, and briefs, and also suitable for middlewear and outerwear.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Polyester fiber -   2 Hydrophilic polyester resin treatment agent molecule -   2 a At least part 2 a of the polyester group -   2 b Hydrophilic group -   3 Antibacterial agent 

1. A fiber structure comprising polyester fibers and a hydrophilic polyester resin treatment agent, wherein part of a molecule of the hydrophilic polyester resin treatment agent is absorbed in at least part of the polyester fibers, and the remainder of the molecule extends along the surface of the polyester fibers to hydrophilize the surface, and wherein the fiber structure has the properties below: (1) antifouling properties of grade 4 or higher according to the gray scale assessment specified in JIS L 0805 (2005), determined using the fiber structure prepared by applying 200 g of muddy water, which is a mixture of normal staining soil and sand and distilled water at a ratio of 1:1, to the fiber structure, followed by standing for 24 hours, washing according to the method 103 specified in JIS L 0217 (1995), and drying; (2) water absorbability of 10 seconds or less according to the falling-drop method specified in JIS L 1907 (2004); and (3) diffusivity of 55 minutes or less according to the diffusible residual water content test, method A-1, specified in ISO 17617 (dropping 0.6 mL of water).
 2. The fiber structure according to claim 1, wherein the hydrophilic polyester resin treatment agent is a linear block copolymer in which a polyester group and a hydrophilic group are linked together at their terminals, and the hydrophilic polyester resin treatment agent has a molecular weight of 5000 to
 8000. 3. The fiber structure according to claim 2, wherein the polyester group has a molecular weight of 200 to
 1000. 4. The fiber structure according to claim 1, wherein the fiber structure further has the properties below: (4) antibacterial properties of 2.2 or more, which is an antibacterial activity value measured based on the antibacterial property test specified in JIS L 1902 (2015).
 5. The fiber structure according to claim 4, wherein the fiber structure further comprises an antibacterial agent that is fixed to the surface of the molecule of the hydrophilic polyester resin treatment agent on the polyester fibers.
 6. The fiber structure according to claim 4, wherein at least part of the antibacterial agent is absorbed in at least part of the polyester fibers.
 7. The fiber structure according to claim 4, wherein the antibacterial agent has a molecular weight of 200 to
 1000. 8. The fiber structure according to claim 1, wherein the fiber structure comprises at least one selected from a knitted fabric and a woven fabric, and the knitted fabric has diffusivity of 55 minutes or less, and the woven fabric has diffusivity of 45 minutes or less according to the diffusible residual water content test, method A-1, specified in ISO 17617 (dropping 0.6 mL of water).
 9. A method for producing a fiber structure comprising polyester fibers and a hydrophilic polyester resin treatment agent, wherein part of a molecule of the hydrophilic polyester resin treatment agent is absorbed in at least part of the polyester fibers, and the remainder of the molecule extends along the surface of the polyester fibers to hydrophilize the surface, and wherein the fiber structure has the properties below: (1) antifouling properties of grade 4 or higher according to the gray scale assessment specified in JIS L 0805 (2005), determined using the fiber structure prepared by applying 200 g of muddy water, which is a mixture of normal staining soil and sand and distilled water at a ratio of 1:1, to the fiber structure, followed by standing for 24 hours, washing according to the method 103 specified in JIS L 0217 (1995), and drying; (2) water absorbability of 10 seconds or less according to the falling-drop method specified in JIS L 1907 (2004); and (3) diffusivity of 55 minutes or less according to the diffusible residual water content test, method A-1, specified in ISO 17617 (dropping 0.6 mL of water), the method comprising: subjecting an untreated fiber structure to immersion heating in an aqueous solution containing the hydrophilic polyester resin treatment agent to make part of the molecule of the hydrophilic polyester resin treatment agent absorbed in at least part of the polyester fibers and the remainder of the molecule extend along the surface of the polyester fibers to hydrophilize the surface.
 10. The method according to claim 9, wherein the immersion heating comprises heating from room temperature to a temperature ranging from 110° C. to 135° C. and keeping the temperature for 20 to 120 minutes, followed by cooling, and water washing.
 11. The method according to claim 9, wherein in the immersion heating, an antibacterial agent is added in the same bath with the aqueous solution.
 12. The method according to claim 9, further comprising, after the immersion heating, padding with an aqueous solution containing an antibacterial agent, and heating.
 13. The method according to claim 9, wherein in the immersion heating, a disperse dye is added in the same bath with the aqueous solution. 